Gaseous fuel engines are known for their ability to burn clean relative to their compression ignition engine counterparts. However, gaseous fuels are well known for the difficulty in attaining successful ignition. Some gaseous fuel engines utilize a spark plug, whereas other engines are known for utilizing a small amount of distillate diesel fuel that is compression ignited to in turn ignite a larger charge of gaseous fuel. In these engines, the gaseous fuel may be supplied to the engine intake manifold or metered directly into individual cylinders where it is mixed with air prior to being ignited responsive to the pilot diesel injection near top dead center. While this strategy may reduce NOx due to a cooler combustion, hydrocarbon emissions may be relatively high and there is no ability to control combustion characteristics, such as reaction rate, to accommodate different engine operating conditions.
U.S. Pat. No. 7,373,931 teaches a dual fuel engine that utilizes a small quantity of compression ignited distillate diesel fuel to ignite a larger charge of gaseous fuel injected after ignition. This reference teaches the use of a fuel injector with nested needle valve members to facilitate injection of both the gaseous and liquid fuels from the same injector into each engine cylinder. In other words, the patent owner teaches direct injection of gaseous fuel into the engine cylinder after a pilot quantity of diesel fuel has been injected and ignited. While the reference claims that this strategy provides improved efficiencies over the counterpart gaseous fuel engines discussed previously, other emissions problems and power inefficiencies, especially at higher speeds and loads may be present.
Regardless of whether the fuel injector is designed to inject one or two different fuels, many considerations must be weighed in considering the viability and competitiveness of a given design. For instance, among these considerations are static leakage and speed of injector response. With regard to the former, excessive leakage of pressurized fuel during times of no injection is equated with waste and higher costs of operation. With regard to the latter, the ability of a fuel injector to quickly respond to electrical commands to end an injection, reset and be ready for a subsequent, possibly close coupled, injection can bear on the fuel system's viability for application in a given engine. For instance, if a fuel injector delays too long between end of current to an electrical actuator and the actual end of injection, and then requires a relatively lengthy delay in resetting pressures within the fuel injector for a subsequent injection event, the fuel injector may not even possess the ability to perform certain injection sequences that may be desirable in a given engine application.
The present disclosure is directed toward one or more of the problems set forth above.